1. Field of the invention
The present invention relates to a plasma etching method and a plasma etching apparatus, and more specifically to a plasma etching method and a plasma etching apparatus, for preventing particles generated in an etching, from depositing on a substrate.
2. Description of related art
In manufacturing a semiconductor device, it is in many cases that a plasma etching apparatus is used for the purpose of executing a dry etching by use of a reactive plasma gas under a low pressure . In the following, an example of a prior art plasma etching apparatus will be described with reference to the drawings. FIG. 6 is a diagrammatic sectional view for illustrating a plasma etching apparatus generally used in a semiconductor device manufacturing factory. The plasma etching apparatus generally indicated with Reference Numeral 10 includes a processing chamber 12 for processing a substrate by an etching, a lower electrode 16 located within the processing chamber 12 for holding a substrate 11 put on an upper surface thereof, and an upper electrode 18 located to face the lower electrode 16 and having a discharge surface for generating an electric discharge between the upper electrode 16 and the substrate held on the lower electrode 16.
The lower electrode 16 includes an electrostatically attracting electrode 15 for holding the substrate 11 by action of an electrostatic attraction, an insulating plate 24 provided under the electrode 15, and a lower electrode body 17 provided under the insulating plate 24. The electrostatically attracting electrode 15 is connected to a DC voltage supply 26, and the lower electrode body 17 is connected to a high frequency voltage supply 28. The upper electrode 18 has a gas introducing path 22 for introducing a process gas and a purge gas, and gas nozzles 22 provided in a lower surface of the upper electrode 16 and over a region positioned just above the substrate. This upper electrode 18 is connected to ground.
Ordinarily, one evacuation port 23 is provided in a bottom of the processing chamber 12, and a feeding port 30 is provided a side wall of the processing chamber 12 for feeding the substrate 11.
FIG. 7 is a graph for illustrating an operating condition of the plasma etching apparatus 10 at the time of etching the substrate in the plasma etching apparatus 10, corresponding to one cycle of the substrate processing. In the plasma etching apparatus 10, a highly reactive process gas such as chlorine is introduced through the gas nozzles 22 of the upper electrode 18 into the processing chamber, and when a pressure has reached a predetermined constant pressure, a high frequency voltage is applied between the upper and lower electrodes to bring the process gas into a plasma condition, with the result that an etching is carried out. If the etching is completed, the application of the high frequency voltage and the supplying of the process gas are simultaneously stopped, and after a few seconds, a less reactive halogen gas is introduced as a purge gas.
However, in an LSI manufacturing process, in particular, in a process for etching a metal film by a plasma gas, generated particles have become a large cause for lowering the yield of production and the operating efficiency of the apparatus. A main cause of generation of the particles is that reaction products deposited on an inside of the plasma etching apparatus peel off and drop on the substrate. Accordingly, it is difficult to completely prevent the generated particles from depositing on the substrate. Under this circumstance, a method for causing the generated particles not to deposit on the substrate, or an apparatus having a function of causing the generated particles not to deposit on the substrate, have been developed. These method and apparatus are disclosed in Japanese Patent Application Pre-examination Publication Nos. JP-A-59-119839, JP-A-60-195937, JP-A-04-250621, JP-A-05-029272, JP-A-05-267234, JP-A-07-058033, JP-A-08-115903 and JP-A-06-122978 (an English abstract of these Japanese patent publications is available and the content of the English abstract of is incorporated by reference in its entirety into this application).
JP-A-59-119839 and JP-A-60-195937 propose to hold the substrate to be processed, downward or vertically, so that the particles falling by gravity is prevented from depositing on the substrate. JP-A-04-250621 propose to provide a cover on an electrode moving part and a periphery of a metal sealing, in order to prevent the falling particles from spreading in the inside of the vacuum chamber. JP-A-05-029272 proposes to mount a cover for covering the substrate just after the completion of the processing, so as to prevent the particles from falling on the substrate. These Japanese patent publications prevent the particles from falling on the substrate.
On the other hand, JP-A-05-267234 and JP-A-08-115903 propose a means for positively moving the particles thereby to prevent the particles from depositing on the substrate. JP-A-05-267234 electrostatically removes the particles by means of a dust collecting electrode. JP-A-08-115903 provides a means for preventing the flow of process gas from being directed from the working electrode to the substrate, thereby to prevent the particles included in the gas from reaching the substrate.
As combination of the above mentioned methods, JP-A-07-058033 proposes to provide an electric precipitator and a cover for covering the substrate just after the completion of the processing, so as to prevent the particles from reaching the substrate.
JP-A-06-122978 proposes to introduce the purge gas between the substrate and the high frequency electrode after the application of the high frequency voltage is stopped, and to cause the particles to reach the surface of the substrate with a few seconds, whereby the particles are prevented from depositing on the substrate surface after the film deposition.
However, the prior art methods and apparatuses disclosed in the above referred Japanese patent publications need to modify the machine or to add parts, so that the mechanism of the machine becomes complicated. In addition, the machine cost becomes high. This problem will be discussed in the following.
In order to change the substrate holding direction, it is necessary to mount heavy parts such as a feeding mechanism, a working electrode and a wafer holding mechanism, on an upper portion of the apparatus, or to hold these parts vertically. As a result, a new problem occurs in connection with a stable operation of the apparatus Furthermore, since it is necessary to strongly make a frame for supporting these heavy parts, the apparatus becomes large in size. Moreover, the substrate feeding mechanism becomes complicated. In addition, after completion of the process, in order to cover the substrate with a cover or in order to electrostatically attract the particle, it is necessary to provide a moving mechanism near to the substrate within the apparatus. Because of this, there is possibility that the particles are generated by the moving mechanism. Furthermore, provision of these mechanisms results in a further enlarged size of the apparatus.
On the other hand, the provision of the cover for preventing the falling particles from spreading in the inside of the vacuum chamber, and the control of the direction of the flow of process gas, cannot sufficiently prevent the particles (dust) peeled off from the upper electrode, from falling and depositing on the substrate.
Under the above mentioned circumstances, there are demanded a plasma etching method for effectively preventing the particles generated in the plasma etching apparatus, from reaching and depositing on the substrate, by adding a simple mechanism without enlarging the size of the processing apparatus, and a plasma etching apparatus capable of carrying out the method.